regulations governing construction vehicles are not as strict as those for passenger cars and trucks but they do exist. As a result, energy consumption and the environment are high priority issues for Volvo CE. The power is supplied by Volvo’s well-proven truck engines, but it is not possible to simply install a truck engine in a wheel loader. Construction vehicles differ from trucks in two major ways:

• The engine has to power not only the vehicle but also a large hydraulic pump, which in turn powers the bucket, crane, and other equipment.

• The vehicle is often at a standstill or operating slowly, which means that there is no headwind to help cool the engine.

Previously, truck engines would be rebuilt to suit the different operating conditions of a construction vehicle. With today’s computer-controlled engines, it is now possible to make many of the necessary adaptations via the software. However, not everything can be changed this way.

“We have to cram a lot of functions into small spaces,” Jens says. “But the more compact our designs become, the more important it is to manage the heat issue.”

Reliability is cRucialYet another difference is that construction

Volvo ce – cooling engines without a headwind

How can you develop construction vehicles when a vital ingredient that is normally taken for granted is basically missing? What’s lacking is any headwind, which is just one of the challenges faced by Volvo Construction Equipment in Eskilstuna.

The company develops wheel loaders and also manufactures components for wheel loaders, haulers and road graders. The machines are assembled in a handful of factories in Europe, the United States and South America.

Purchasers of wheel loaders tend to regard them as the equivalent of giant levers on wheels. This attitude places special demands on the development work behind the machines. The goal is to exert the biggest possible force on the most weight by using the smallest possible machine and the lowest energy consumption.

“What’s most important are the materials’ physical properties like ultimate tensile strength and vibration resistance,” explains Jens Hjortsberg, who is in charge of calibration at the Eskilstuna factory.

PRioRity on the enViRonment Temperature is another increasingly important factor, as legislation becomes stricter with regard to energy consumption and emissions, especially of carbon dioxide. Current

“Construction vehicles are expected to start in all weathers. That places extra high demands on us,” says Jens Hjortsberg of Volvo in Eskilstuna.

PentRonic Scandinavia’s largest manufacturer of industrial temperature sensors Vol. 2 no. 5 2009

vehicles are expected to start and function in rugged environments and to operate within a greater temperature range than other vehicles.

When the thermometer drops below -40 °C our entire society depends on the ability of wheel loaders to start their engines and be able to remove snow. Equally, we expect the same vehicles to function well and provide their operators with a decent working environment in the desert heat. For this reason, the Volvo development centre in Eskilstuna has its own climate chamber.

Volvo CE’s development work involves taking many different measurement readings with close tolerances, so the company has its own calibration laboratory for temperature.

“We have a water bath with a Pt100 working reference and a dry block calibrator with a type N thermocouple,” Jens says.

Focus on the FutuRe As regulations become more stringent, calibration is increasingly important. Pentronic is involved as a supplier of calibration equipment, temperature sensors and calibration services.

Just like all other forms of ground, air and water transport, construction vehicles are being equipped with new kinds of fuels and engines. Volvo CE has already presented concept loaders with hybrid engines and has more projects underway.

Pentronic News visited Eskilstuna shortly after the long summer vacation. Orders were down as a result of the economic crisis but there was no sign of this in the development department, where everyone was hard at work preparing for the future. As a long-term trend, more and more construction vehicles will be required to build a society that is sustainable in the long term. In working to make this a reality, Volvo Construction Equipment must keep on monitoring temperatures.

“Our calibration laboratory isn’t large but it functions well,” Jens says. The lab has a dry block calibrator and a water bath.

The advanTage of uSing a mulTiTube:

one hole for nine measuring points With its multiple thermocouple points, the multitube is one of Pentronic’s more complex sensors. It is used when customers want a single sensor to measure temperatures at a number of different physical locations within chemical processes.

“The multitube sensor is not complicated in itself – the challenge is to ensure that it is rugged enough to continue functioning well in a difficult measuring environment,” comments Per Wilén, sales engineer at Pentronic.

The sensor was developed for a chemical reactor. In the specific case in question, so many temperature sensors were needed that using normal individual ones would have created a huge tangle of sensors and cab les. All in all, the process required 90 measuring points.

The solution was a six-metre-long tube. It is six millimetres in diameter and contains nine sheathed thermocouples. The tube itself is made of a material which is thin enough that it can be bent, thereby making the installation easier.

The challenge lies in ensuring that the tube is completely sealed so that the chemicals cannot adversely affect the thin thermocouples. In addition, the thin sheathed thermocouples are in themselves sensitive, and so special routines must be used in their manufacture and final inspection.

“There cannot be any damage to the sheaths or wires,” Per explains. “That would

The multitubes in the photo were designed and manufactured by Pentronic. They allow for multiple measuring points with fewer insertion holes. In this case, six tubes are being used to monitor the process inside a tank at a chemical plant. About 50 measuring points are accessed via a single opening in the tank.

probe tips are located at 100-125 mm intervals but longer or shorter intervals can be used with equal success. A tube that is 6 mm in diameter can contain a maximum of 10 thermocouples but wider tubes will hold more. However, the bending moment of the tube will decrease as the diameter increases.

The big advantage of the multitube is that the temperature can be measured at multiple positions by using just one insertion point. This means less installation time and fewer holes that can weaken process vessels and other containers.

Measuring temperature, force and weight involves many similarities. Accordingly, it is no coincidence that Pentronic has begun working with Flintec, which has been a sister company within the Indutrade group for just over a year.

Flintec was founded by the Swedish entrepreneur Rune Flinth and is now a world leader in the measurement of force and weight. The company’s sensors can be found in many scales used in the retail sector worldwide. Flintec is now also growing within other, more high-tech segments.

“There are major similarities when measuring temperature, weight and force,” explained Flintec’s CEO David Weeks during a visit to Pentronic in mid-September.

collision FoRce Anyone who wants concrete proof of this need only go to his nearest supermarket and examine the weigh scales, which are required by law to undergo traceable calibration at regular intervals.

Flintec develops and manufactures various types of strain gauges and associated equipment, which are often supplied as

helping to develop the measurement of weight and force complete units together with the associated electronics and software. The company’s biggest customer demand is for solutions to measurement problems.

Flintec equipment is used to measure weight and force. Examples of end use areas include: weighing in industrial processes such as during the filling of food and pharma packets, in various types of vehicles, in the health care sector, and for crash testing vehicles.

Just like temperature, it is becoming

put at risk the whole concept of combining a number of thermocouples within one unit.”

To protect them during shipment, the multitubes are shipped fully extended in long, narrow, sturdy wooden boxes.

“The multitubes are an interesting solution for measuring at multiple points in processes, tanks, and so on,” Per says.

Inside Pentronic’s original multitube, the

increasingly important to measure weight and force in order to increase process efficiency, improve quality, and reduce energy consumption.

helPing to suPPoRt otheR bRands As well as their similar technology, there is another similarity between Flintec and Pentronic. Both companies develop and make measurement equipment for global leaders in many industries. Both companies’ products can be found inside the casing of products made by many other brands, where they act as guarantees of precision and reliability.

“We’ve already discovered that Pentronic’s technology can be highly useful to us,” David said. “I hope Pentronic will see the same possibilities in Flintec.”

Both companies have been working together for many years in one area. Pentronic supplies temperature sensors for ships that transport bananas around the world. Those same bananas are later weighed in super-markets using equipment from Flintec, and in both cases the resulting measurements are traceable to national standards. The result is satisfied consumers with bananas of the right consistency, taste, and weight.

“Pentronic has technology that is also useful for measuring force and weight,” says David Weeks, CEO of Flintec. Both companies are owned by Indutrade.

To express viewpoints or ask questions, contact Professor Dan Loyd, Linköping University

by e-mail to: dan.loyd@liu.se

stRaight FRom the lab

is a surface probe reliable?QUESTION: In order to better monitor our district heating network we plan to install new temperature sensors, especially in a large pipe (DN 1000 size with an outer diameter of 1016 mm and a wall thickness of 11 mm). The average velocity of the water in the pipe is 0.8 – 4.0 m/s and the temperature is 75 – 110 °C. Can we use a surface probe instead of an insert probe to measure the water temperature with less than 1 °C measurement error and little delay?

Sören A

ANSWER: A surface probe measures the temperature on the outside of the pipe. The heat flow from the water to the pipe’s surroundings means that the measured temperature will deviate from the water temperature. In a stationary situation the measured temperature will be lower. There is no general answer regarding the size of this measurement error. However, if we make a number of assumptions we can estimate the measurement error and the dynamic behaviour of the measurement system.

Let us assume that the pipe is insulated. The heat is transferred from the water to the surroundings of the pipe via convection

between the water and the inside of the pipe, plus heat conduction within the pipe wall and within the insulation. If the pipe is surrounded by air, the heat is transferred from the outside of the insulation via convection and radiation to the surrounding air. If the pipe is buried underground, the heat is transferred to the surrounding earth via conduction. Our model assumes natural convection on the outside of the pipe and a temperature of 10 °C.

The water flow in the pipe is turbulent and we assume that the turbulence is fully developed. We further assume that the water temperature is constant across the pipe. The lower the flow

velocity, the greater the measure-ment error. If we as-sume that the pipe is not insulat-ed, these conditions

will result in a measurement error of about 0.5 °C. If the pipe is insulated with the equivalent of 5 cm of mineral wool, the measurement error will be less than 0.05 °C. Both of these readings meet the requirements for measurement error.

In the case of the insulated pipe with the assumptions stated above, we can estimate the response time of the measurement system. If we calculate the step response time, t0.5, for a temperature reduction of the water of 10 °C, the sensor will measure a temperature change of 5 °C after less than 15 seconds. Flow velocities higher than 0.8 m/s will decrease response time even more. A response time (t0.5) of 15 seconds should be acceptable for monitoring a district heating system.There are Pt100 sensors specially designed to take surface measure-ments. It is important to install them under the insulation and with good thermal contact with the pipe. You must inspect the sensor installation regularly because poor surface contact seriously impact the measurement readings.

Questions? ansWeRs !

Pentronic’s laboratory is accredited since 1988

best measurement ability and actual measurement uncertaintyAll accredited calibration laboratories, whatever their size, publicly state their best measurement ability. This ability is the degree of measurement uncertainty that is achieved by a specific laboratory under ideal conditions. This measurement ability is stated in the accreditation documentation

issued to the specific laboratory by the accrediting body.

The laboratory’s measurement ability in specific cases is stated in its accreditation documentation, which is available at Pentronic’s website, www.pentronic.se > Calibration > Accreditation limits, and from

SWEDAC, www.swedac.se. A laboratory will calculate the actual measurement uncertainty in each specific case and state it in the test certificate being issued.

M e a s u r e m e n t uncertainty is calculated by using methods given in the document EA-4/02, which can be downloaded from www.european-accreditation.org.

Pentronic + export = experience Pentronic is Scandinavia’s leading manufacturer of industrial temperature sensors but remains an unknown name to many people. Despite this, its products can be found around the world.

Many of Pentronic’s end customers are located outside Sweden, a situation that has existed for many years.

“We are suppliers to successful export companies both in Sweden and in neighbouring countries,” says Pentronic’s CEO Lars Persson.

The company’s customers include machinery builders in industries like liquid foods, vehicles, pharmaceuticals and energy production. Many are world leaders in their field and have manufacturing facilities both in Sweden and abroad. As a result, Pentronic has acquired considerable expertise in making

worldwide direct deliveries and has developed well-functioning routines for this purpose.

One consequence of this strong export focus is Pentronic’s accredited temperature calibration laboratory.

Formally accredited in 1988, the lab can trace its existence back almost 30 years. It was one of the first private calibration laboratories to be accredited outside the official Swedish national calibration system. The laboratory has contributed greatly both to Pentronic’s temperature expertise in general and to the performance and quality of its sensors.

Another result of this export experience is that Pentronic has classified its sensors for different markets and industries. The company has also developed routines for complying with the legal and administrative requirements of various markets.

Pentronic is small compared with the size

of its customers, although is now owned by one of Sweden’s fastest growing companies, Indutrade. However, Pentronic is one of the largest players within the highly specialised niche of temperature sensors for industrial applications.

“Quite a number of our colleagues in the industry are limited to their own local market,” Lars explains. “Pentronic is one of the few companies to operate globally. The reason for this is also the reason why Sweden has a higher proportion of global companies compared with most other countries. We are a small nation and have to seek out markets outside our borders.”

moRe diRect exPoRtsToday Pentronic’s temperature sensors can be found all over the world, primarily as components in large machines. However, direct exports of the company’s sensors have increased significantly in recent years to markets such as China.

It is crucial that the temperature sensor is in good contact with the pipe, e.g. by means of a spring clip. Heat sink compound facilitates the heat transfer.

SE-590 93 Gunnebo, SwedenFax. +46 490 237 66, Tel. +46 490 25 85 00

info@pentronic.se, www.pentronic.se

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too shallow an immersion depth causes measurement errorThe new IEC60751:2008 standard proposes a number of type tests for Pt100 sensors. One test establishes the minimum immersion depth. Another establishes the response times. Let us examine what lies behind these tests.

According to IEC60751:2008 [Ref 1], the

In both cases, the measuring equipment showed stable readings. This situation can make an operator believe that the stationary values are the true ones.

The response time is also affected by the probe tip design and the sensor’s heat conduction ability. Diagrams 3A and B show the measured response time curves for both sensor designs. Not unexpectedly, the sensor with the

air gap responded significantly more slowly than the sensor with the metal filling to an instantaneous temperature step (immersion). The reason is of course the limited ability of the former to conduct heat.

aFFects the ResPonse time IEC60751:2008 recommends the following conditions for testing response times. The medium is water or air with a flow velocity of > 0.2 m/s and (3 ± 0.3) m/s respectively. Normally, the time it takes to achieve half the final value is stated as the response time. Note that the measuring system within which the sensor is to be used has its own response time (the system response time). The sensor forms only part of this system.

The design of the temperature sensor influences all its properties with regard to the minimum immersion depth and possible response time. For this reason, in critical situations it is important to study and compare the properties of different sensor designs under the same conditions, or to clearly specify the desired properties and have a sensor custom made for the purpose.

[Ref 1] See www.pentronic.se > Pentronic News > Pentronic News Archive > Pentronic News 2009-4

definition of the minimum immersion depth for a sensor is the depth at which the signal has decreased by 0.1 °C compared with the immersion depth used during the tolerance acceptance test. Further, the standard speci-fies that the measuring medium shall be water with a temperature of at least 85 °C. No flow velocity is stated but at temperatures above 85 degrees water has a strong self-circulation. The sensor’s terminals are located at room temperature, which temperature laboratories set at 23 °C. From this starting point, the sensor is then raised step by step out of the water. The immersion depth at which the temperature has dropped by 0.1 °C shall then be stated as the minimum immersion depth.

The basic cause of falling temperature readings taken by a sensor at shallower and shallower immersion depths is the temperature difference between the sensor’s two end points. This difference creates a heat flow from the warmer end point to the colder one. Heat is transported along the tube via conduction and is emitted to the surroundings via radiation and convection. The shallower the immersion depth, the greater the temperature difference per unit of length in the tube. (See diagram 1.)

Where the sensor exits the process, or the water bath in the test, the temperature gradient (degrees per unit of length) is steepest. This is where the biggest drop in temperature occurs.

You can avoid significant measurement errors by first trying to establish a greater immersion depth, that is, by placing the sensor in a zone that has little difference in temperature. (Cf. diagram one.)

aPPlies to all sensoRsIt must be emphasised that all temperature sensors have a minimum immersion depth at which the temperature reading has changed by 0.1 °C. What distinguishes tempera-ture sensors from each other is factors like their physical design and dimensions, the properties of the medium, and the flow velocity. A thin thermocouple wire in water has a very shallow minimum immersion depth.

Diagram 2 shows a practical experiment that was conducted in Pentronic’s temperature laboratory using DIN Form B-type process sensors. Different versions of the sensors were immersed to varying depths in a stirred calibration bath. Using a Ø 6 mm measuring insert mounted in a Ø 10 mm outer protective tube, varying readings were achieved depen-

ding on the different probe tip designs.It was clear that the air gap

between the sensor and the outer protective tube exerted a serious negative effect at shallow immersion depths. The sensor model which had a metal filling had a very small drop in temperature up to the Pt100 resistor. The other model showed a grea-ter temperature drop in the air gap and thereby a lower temperature in the resistor.

Diagram 2. The ability to transfer heat between the probe tip and the Pt100 resistor is important at shallow immersion depths. For example, at a 75 mm immersion depth the blue design decreases by 0.25 °C and the red one by 1 °C. The explanation is the use of a metal filling in the blue probe instead of the air gap plus a powder filling in the red probe.

Diagram 1. IEC defines the minimum immersion depth LMIN for a sensor whose reading has decreased by 0.1 °C compared with the tolerance acceptance test reading taken at insertion point L. The diagram shows both alternatives. The cause of measurement error in shallow immersion depths is the greater temperature gradient in the protective inner and outer tubes.

Diagram 3. The air gap is a major obstacle for heat transfer in dynamic conditions such as step response. Diagrams A and B have been produced in identical conditions and have the same scale.